Field of the Invention
The present invention is broadly concerned with novel, multiple patterning methods that utilize a shrinkable composition to form spacer structures.
Description of the Prior Art
Due to delays in developing the next generation of 193-nm immersion technology and extreme ultraviolet lithography (EUVL), double patterning using currently available tools is the only lithographic technique planned for use from 2008 to 2012 for the 32- and 22-nm half-pitch nodes. Self-aligned spacer technology is one double-patterning technology under extensive investigation. The spacer approach has the advantage of requiring only one lithographic exposure, which avoids the serious issue of overlay between successive exposures. Spacers are created by depositing a coating on prepatterned features and then etching to remove those portions of the film present on the horizontal surfaces, which leaves the spacer film layer lining only the sidewalls. The original patterned feature is then removed to leave only the spacers. Because two spacers are created for every line, the line density doubles. As a result, 32-nm or smaller dense lines can be fabricated.
There have been prior attempts using spacer technology based on films applied using CVD (chemical vapor deposition) processes. The process involves several CVD steps to prepare the layers under the photoresist before photolithography. After photolithography, several steps of etching are used to open the underlayers to prepare the template. After the template is prepared, CVD is used to apply a conformal coating, which can be further etched to form spacers. The need for so many steps makes the process costly and inefficient. Furthermore, the accumulation of layers leads to the inability to control CD (critical dimension).
Other attempts have been made to double the frequency or pitch of small features using materials and a process called resolution enhancement lithography assisted by chemical shrink (RELACS). The RELACS process is based on a crosslinking reaction induced by acid that is diffused out from the resist and involves four steps: spin-coating; blanket exposure; baking; and developing. The primary application of the technology has been to shrink contact holes, which depends upon a chemical interaction induced by the resist. This approach is not useful for forming small lines, but rather only has applicability to double the frequency of large (>100-nm) lines fabricated by KrF (248-nm) technology because the KrF RELACS process is performed under relatively mild conditions (<120° C.). However, the fabrication of 32-nm lines is based on ArF (193-nm) technology. The mobility of acid in an ArF resist is extremely low, and the ArF RELACS process requires a high baking temperature (>120° C.), which will distort the original resist lines. Thus, this process lacks potential for any practical applications.